The present invention relates to an apparatus for producing pellets of plastic, rubber, ceramic, a composite of them or the like.
The inventor of the present invention has disclosed two kinds of pellet production apparatus in Japanese Patent Publication Nos. 55-1166 and 56-12490.
The apparatus disclosed in the Publication No. 55-1166 is basically made up of a combination of an ordinary screw type extruder with a specifically designed pellet forming device. The pellet forming device is composed of a stationary cylindrical sheath member formed by a hollow cylinder having on its cylindrical surface many orifices as nozzles and of a grooved cylindrical rotor formed by a cylinder having on its cylindrical surface some lengthwise grooves and corresponding lengthwise ridge portions. The grooved cylindrical rotor, being inset in the stationary cylindrical sheath member, is sized so that the lengthwise ridge portions may rotatably be fitted to the inner surface of the stationary cylindrical sheath member. The thus constituted pellet forming device is attached to the extruding end of an screw type extruder with said stationary sheath member fixed to the body of the extruder and with said grooved rotor coaxially connected with the screw part of the extruder. In such an entire constitution of the apparatus, a pellet material extruded into the pellet forming device from the extruder is pushed out from the orifices of the sheath member through the grooves of the rotor, and then cut off by the ridge portions of the rotor as it rotates together with the screw of the extruder. Thus, many pellets can be produced at a time and continually.
However, this apparatus has proved to have a disadvantage that the length of produced pellets is not determined only by the mechanical structure of the pellet forming device, but largely influenced by the inner pressure and screw rotation speed of the extruder or the viscosity of the material.
The apparatus, which is disclosed in another Publication No. 56-12490, is an extruder whose extrusion end comprises many extrusion nozzles and a cutter or cutters. According to this apparatus, a plurality of continuously extruded cord-like pellet materials are cut into pellets by the cutter or cutters.
A decisive disadvantage of this apparatus is that the productivity is low owing to the use of a cutter or cutters, especially in producing such small pellets as are, for example, 1.5 mm in diameter and 2 mm in length. Application of this apparatus is limited because of a recently increasing demand for such small-sized pellets.